If the selling price of 50 articles is equal to the cost price of 40 articles, then the loss or gain percent is:

A. 20% loss
B. 20% gain
C. 25% loss
D. 25% gain
Explanation:
Let C.P. of each article be Re. 1.
Then, C.P. of 50 articles = Rs. 50;
S.P. of 50 articles = Rs. 40.
Loss % = 10/50 * 100 = 20%